Suspension or liquid dispersion systems in which fine particles are dispersed in a continuous-phase solvent are divided into the following two categories according to shear rate characteristics: Newtonian fluids that show a constant viscosity regardless of a change in the shear rate; and non-Newtonian fluids whose viscosity changes when the shear rate changes.
A shear thickening fluid (STF), a kind of non-Newtonian fluid, is a fluid such as a colloidal suspension which contains solid particles dispersed in a liquid dispersion medium and which reversibly changes from a liquid state to a solid state due to its rheological properties when the shear stress or shear rate thereof increases to rapidly increase the viscosity.
The shear thickening fluid is usually in a liquid state, and changes to a solid state when a sudden shock is externally applied thereto. Due to this property, studies focused on impregnating the shear thickening fluid into fibers to provide bullet-resistant or stab-resistant materials are currently being actively conducted.
The shear thickening fluid is generally prepared as a sol-type dispersion or suspension by mixing nano-sized silica particles as solid particles with the polar solvent polyethylene glycol as a dispersion medium. In order to bullet-resistant or stab-resistant performance using the shear thickening fluid, it is required to increase the rate of filling of inorganic particles in the shear thickening fluid or the rate of impregnation of the shear thickening fluid in fibers. If the rate of filling of inorganic particles or the rate of impregnation of the shear thickening fluid is increased as described above, the weight of the resulting bullet-resistant material can be greatly increased, making it difficult to provide lightweight materials, the resulting bullet-resistant material can absorb a certain amount of shock, but a significant amount of shock will be applied to the human body.
Thus, there is a need for studies on shear thickening fluids having an improved ability to absorb external shock while having improved viscosity properties.